This application claims priority under 35 U.S.C. xc2xa7119 to patent application Ser. No. 0103255-6 filed in Sweden on Oct. 1, 2001, the entire content of which is hereby incorporated by reference.
This invention relates to a cutting insert, intended for chip removing machining, of the type that comprises a body that is delimited by on one hand two opposite, first and second surfaces, which in the operative state of the cutting insert form an actively chip removing top surface and an inactive bottom surface, respectively, and on the other hand at least one side surface serving as a flank surface, which extends between said first and second surfaces. A cutting edge is formed between the flank surface and at least one of said first and second surfaces, in connection with which a cutting geometry surface extends, which is generally parallel to an imaginary reference plane through the cutting body. The cutting geometry surface, counted from the cutting edge, includes a primary chamfer which transforms into a chip removing surface, which is inclined in the direction inwards/downwards in order to permit sinking of a chip being under formation, and which transforms into a deflection surface arranged to be met by the chip and at least initiate deflection or guiding away of the same from the cutting insert.
If the cutting insert is single-sided, there is a cutting geometry surface present merely on the top side of the body, while the bottom side has a plane support surface. If the cutting insert is double-sided, such cutting geometry surfaces are present at the top as well as at the bottom of the cutting insert.
Cutting inserts of the above generally mentioned kind may be of a round (circular or oval) as well as a polygonal basic shape. In the last-mentioned case, the cutting body is defined by at least three (usually plane or slightly curved) side surfaces or flank surfaces that extend between said first and second surfaces, whereby nearby flank surfaces transform into each other via a convexly rounded nose to which at least one cutting edge connects, which is divided in a plurality of segments having different radii, viz. a first edge segment in immediate vicinity of the actual nose, a second edge segment that is located on one side of the nose, a third edge segment, located on the opposite side of the nose, which is arranged to release at a certain clearance angle from a machined surface on the workpiece, as well as a fourth edge segment located between the first and third edge segments, that fulfils the purpose of smoothening and facing the machined surface of the workpiece.
Cutting inserts of the kind in question, that constitute replaceable wearing parts and are detachably mounted in different kinds of holders for cutting tools, may be used industrially for highly varying purposes, such as milling, drilling, broaching, turning and the like. The workpieces that are machined usually consist of metal, whereby the cutting inserts are made from a hard, hardwearing material, such as cemented carbide, silicon nitride, aluminum oxide, etc., while the holders of the tools are made from a more elastic material, in particular steel.
In previously known cutting inserts, the xe2x80x9ctopographyxe2x80x9d of the cutting geometry surface, i.e., the elevation differences between the highest and lowest located points, respectively, of the cutting geometry surface have been coarse or markedly undulating, on one hand so far that the angle of inclination of the chip removing surface in connection with the primary chamfer of the edge has been comparatively large (approx. 20xc2x0 or more), and on the other hand so far that the elevation difference between different tumblings or ridges having a chip breaking or steering function and valleys or bottoms situated deepest of the cutting geometry surface have amounted to measures being considerable in this context (0.5 mm or more). In said tumblings and ridges, respectively, protruding high up from the bottom regions of the cutting geometry surface, heat concentrations occur, which inter alia lead to crack formations in the cutting insert, and thereby shortening the service life thereof.
For one of the above-mentioned fields of application, viz. turning, the interaction between the feeding of the cutting insert and the design of the cutting edge is of great importance for several aspects of the operation outcome. Generally, a nose having the largest possible radius should be chosen at rough turning, with the purpose of achieving a strong cutting edge. However, too large a nose radius may cause vibrations and detrimental generation of heat. Therefore, at smooth turning, a smaller nose radius is advantageously selected; usually smaller than 2 mm. A disadvantage of a small nose radius, however, is that the wear of the cutting insert is hastened, whereby the service life and performance thereof are deteriorated.
Another factor that is affected by the interaction between the nose radius and the feeding is the surface finish of the rotary workpiece. Particularly important in this respect is the surface smoothening edge segment that is present on at least one of the sides of the actual nose or on both sides of the nose. Investigations that form the basis of the present invention have shown that the so-called tangent point of the smoothening edge segment has a particularly great importance for the surface finish. This tangent point is the geometrical point along the smoothening edge
In previously known turning inserts, (see, for instance, Publication WO 95/00272; U.S. Pat. No. 6,217,263; U.S. Pat. No. 5,226,761; Swedish Applications SE-9401732-4; SE-9702501-9 and Russian Document SU-1782196) the surface smoothening edge segment is usually arched and extends as a continuous line between on one hand, the point where this edge segment directly or indirectly transforms into the nose edge itself and on the other hand, the point where the same directly or indirectly transforms into the edge segment that releases at a certain clearance angle from the machined surface of the workpiece. In practice, the length of the surface smoothening edge segment should substantially be equally large as the feeding, i.e., the axial distance that the cutting insert covers during one revolution of rotation of the workpiece.
An annoying circumstance in regards of the surface finish in previously known cutting inserts is that the position of the actual tangent point along the surface smoothening edge segment has not been able to be predetermined in a reliable way. Thus, the actual tangent point may drift in an uncontrollable way between the two opposite ends of the edge segment and in this connection give rise to varying surface finish.
In order to guarantee an acceptable surface finish, the feeding has in previously known cutting inserts been limited to maximally 0.6 or 0.7 mm/rev. Theoretically, it is feasible, per se, to enable high feedings with straight smoothening edge segments, but in practice this way is objectionable so far that straight edge segments with a smoothening function involves large radial cutting forces with the ensuing risk of vibrations and high generation of heat.
Aims and Features of the Invention
The present invention aims at obviating the above-mentioned disadvantages of previously known cutting inserts and at providing an improved cutting insert. Therefore, a primary aim of the invention in a first aspect is to improve the cutting geometry surface adjacent to the operatively active cutting edge of the cutting insert, more precisely with the purpose of minimizing the risk of heat concentrations and crack formations in the material in the surface zone of the cutting insert. Another aim of the invention is to provide a cutting insert that generally guarantees an improved surface finish of the machined surface of a workpiece. In the embodiment thereof as turning insert, this possibility should for instance be utilized for radically increased feeding with a retained or even improved surface finish. In an analogous way, the invention should be able to be utilized for general performance increase of cutting inserts having a surface smoothening edge segment also for other machining techniques than just turning, such as milling, drilling, broaching or the like.
At least the primary aim of the invention is attained by a cutting insert for chip removing machining of work pieces. The insert comprises a body having opposite first and second surfaces interconnected by at least one side surface. When the insert is in an operative cutting state, the first and second surfaces form a chip removing top flank surface and an inactive bottom flank surface, respectively. The top flank surface forms a cutting edge with the side surfaces. A cutting geometry surface extends from the cutting edge and includes a primary chamfer extending from the cutting edge and transforming into a chip removing surface. The chip removing surface is inclined in a downwards and inwards direction and transforms into a chip deflection surface for initiating deflection of a chip. The chip deflecting surface forms an angle with a center reference plane extending parallel to the top and bottom surfaces, the angle being no greater than 18xc2x0. A difference in elevation between the chip deflection surface and a highest point of the primary chamfer being no greater than 0.20 mm.